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<html lang="en">
<head>
    <meta charset="UTF-8">
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    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="./js/jquery-3.4.1.js"></script>
</head>
<body>
    <select name="" id="con1">
        <option value="请选择">请选择</option>
        <!-- <option value="河南">河南</option>
        <option value="河北">河北</option>
        <option value="山东">山东</option> -->
    </select>
    <select name="" id="">
        <option value="请选择">请选择</option>
    </select>
    <select name="" id="">
        <option value="请选择">请选择</option>
    </select>
    <script>
        var arr1 = ['河南','山东','河北'];
        var arr2 = [['信阳','郑州','焦作'],['临沂','济南','青岛'],['石家庄','保定','唐山']];
        var arr3 = [[['淮滨县','固始县','平桥县'],['金水区','二七区','高新区'],['山阳区','武陟县','沁阳市']],
        [['兰山区','沂水县','兰陵县'],['历下区','天桥区','槐荫区'],['黄岛区','即墨区','城阳区']],
        [['长安区','桥西区','鹿泉区'],['雄县','清苑区','莲池区'],['乐亭县','迁西县','迁安县']]];
        for(var i=0;i<arr1.length;i++){
            $('select:eq(0) option').after('<option>'+arr[i]+'</option>');
        }
    </script>
</body>
</html>